Fuel delivery systems of the subject character typically include a pump for delivering fuel under pressure from a supply to a fuel consumer, such as an internal combustion engine. Excess fuel at the engine is returned to the supply tank through a pressure regulator. A check valve is connected between the pump and the engine for preventing back-flow of fuel from the engine to the pump when the pump is turned off. Fuel pressure is thereby maintained at the engine, resulting in reduced start-up time. Typically, the check valve includes a valve element biased by a spring against a seat within a fuel passage. That portion of the passage extending from the seat surrounding the valve element is of uniform cylindrical contour so that, after lift of the valve element from the seat, cross sectional area to fluid flow between the valve element and the surrounding wall remains substantially constant and independent of valve lift. U.S. Pat. No. 4,697,995 discloses a check valve of the described construction carried by the housing of a fuel pump, and thus constructed as a unitary assembly with the pump.
Although fuel delivery systems of the described character, as illustrated in the noted U.S. Patent, have enjoyed substantial commercial acceptance and success, improvements remain desirable. For example, positive displacement fuel pumps conventionally employed in automotive engine fuel delivery systems typically are of construction that deliver intermittent fuel flow and/or pressure pulses over and above a constant or average level. These pulsations affect engine operation and can cause noise in the vehicle, and reduction or elimination thereof is desirable. Further, since cross sectional area to fluid flow in prior art check valves of the subject character is substantially independent of valve position, there is a marked tendency for the valve element to oscillate around an average position, thus exacerbating rather than reducing the problem of pressure and flow pulses in the pump output.
A general object of the present invention, therefore, is to provide a check valve that finds particular utility in fuel delivery systems of the subject character, but also enjoys wide application in other flow control environments of similar nature, and that helps reduce or eliminate pressure and flow pulses in the fuel delivery line. Another and more specific object of the invention is to provide a check valve of the described character that exhibits a cross sectional area to fluid flow that increases continuously or substantially continuously, preferably substantially linearly, with fluid pressure and corresponding motion of the valve element against the force of the return spring.